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Science News

Evening star goes black in rare celestial eventAstronomers position themselves to capture crucial measurements as Venus passes across the face of the sun

By Nadia DrakeWeb edition : Tuesday, May 22nd, 2012

On June 5, skywatchers will have their last chance to glimpse a rare celestial spectacle, a “transit of Venus,” in which the planet passes directly between Earth and the sun. Venus will take six hours to march across the star’s face, appearing as an inky black dot in silhouette against the looming solar disk.

After that, the sun-shadowed Venusian outline will disappear until 2117. Because the planet’s orbit is slightly off-kilter, its solar transits come in pairs spaced eight years apart, with more than 100 years between pairs.

During the most recent transit pair of 1874 and 1882, observers around the world focused on triangulating the Earth-sun distance. They tried to time precisely when Venus entered and exited the sun’s disk, so they could calculate the size of the sun (a complicated endeavour, it turns out, since an optical effect that blurred the boundary between planet and sun muddied the timing measurements). The most recent transit happened in 2004 — only the sixth such performance seen through telescopes — and it revealed that large portions of the Venusian atmosphere are visible to Earthly observers.

Now, scientists are hoping not only to study Venus itself during the transit, but are using the crossing to inform observations of far-off exoplanets that similarly betray their presence by passing between their star and Earth. “Over 100 years ago, astronomers couldn’t have anticipated this transit question,” says astronomer Jay Pasachoff of Williams College in Williamstown, Mass., who will observe the transit from Hawaii.

Pasachoff and his colleagues are also deploying nine instruments to locations including Japan, Kazakhstan, and Norway, to study the sunlight filtered through Venus’ toxic clouds.

During the transit the sun will act as a giant light bulb, illuminating Venus’ upper atmosphere and providing information about temperature and aerosols across the planet. The orbiting Venus Express spacecraft can gather data only about isolated portions of the swirling sulfuric acid clouds, begging the question of how the shroud behaves globally. “As temperatures and winds are closely linked, those measurements will be fed into models that aim to explain the exotic dynamics of the Venusian atmosphere,” says astronomer Thomas Widemann of the Paris Observatory, who will join Venus Express team members in Svalbard, Norway to observe the transit against the midnight sun.

When Earth’s little sister passes before the solar backdrop, its planetprint produces the type of dimming that occurs when exoplanets periodically block their stars’ light. Astronomers have been able to study the atmospheres of Jupiter-sized exoplanets, but similar observations of terrestrial planets are still a thing of the future.

Gathering data about a known planet – Venus – will help ground those future observations, says astronomer Paolo Tanga at the Cote d’Azur Observatory in Nice, France. “Maybe one day we will be able to measure the same light that is filtered from the atmospheres of exoplanets – exo-Venuses and exo-Earths,” says Tanga, who will be in Arizona for the transit.

But such observations aren’t so simple. “Big mirrors and sensitive detectors are not good things to point at the sun,” explains planetary astronomer Heather Knutson of Caltech. Instead astronomers will use the Hubble Space Telescope to capture sunlight reflected off the face of the moon during the transit. In that light are signatures of chemical compounds in the Venusian atmosphere, Knutson says. “It’s the first time we can make this measurement for a truly terrestrial planet.”

The shadow of Venus last passed across the sun in June 2004. After another transit by the planet this June 5 and 6, the spectacle will not recur until 2117. Credit: Andjelko Gilvar/ VT-2004 programme; ESO

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Nice Master trigggl. I hope you can see all that you wish. Now more news from science.

Blue light tells plants when to flowerProtein that marks day length also coordinates blooming genes

By Rebecca CheungWeb edition : Friday, May 25th, 2012

As the days become longer in spring, plants know to bloom thanks to an interaction between several crucial proteins and blue light, scientists report in the May 25 Science. The new work describes the molecular mechanics that enables a light-sensitive protein to help switch on a suite of genes that control flowering. Understanding the biology of how plants regulate flowering could be useful for tweaking crops to start producing food earlier in the year.

“We might be able to grow three times or twice as much in a season,” says study coauthor Takato Imaizumi, a molecular biologist at the University of Washington in Seattle.

Generally, plants need to start blooming around the time when most pollinating insects will be buzzing around — such as in early spring — to maximize their chances of reproducing.Scientists have known that plants have higher levels of the blue-light sensitive protein FKF1 toward the end of the day and that the protein is important for tracking day length. It’s also been shown that another protein, called CO, plays a key role in turning on flowering genes.

In the new work, Imaizumi and his team looked at the flowering plant Arabidopsis thaliana. The researchers show that FKF1 helps stabilize the CO protein long enough to turn on flowering. Blue light — a particular wavelength of visible light that is common in sunlight that shines down at the end of a spring day, around the same time there is more FKF1 — enhances the interaction. FKF1 also lowers levels of a protein that normally serves as a brake on blooming.

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ScienceDaily (May 28, 2012) — A new study combining the latest archaeological evidence with state-of-the-art geoscience technologies provides evidence that climate change was a key ingredient in the collapse of the great Indus or Harappan Civilization almost 4000 years ago. The study also resolves a long-standing debate over the source and fate of the Sarasvati, the sacred river of Hindu mythology.

Once extending more than 1 million square kilometers across the plains of the Indus River from the Arabian Sea to the Ganges, over what is now Pakistan, northwest India and eastern Afghanistan, the Indus civilization was the largest -- but least known -- of the first great urban cultures that also included Egypt and Mesopotamia. Like their contemporaries, the Harappans, named for one of their largest cities, lived next to rivers owing their livelihoods to the fertility of annually watered lands.

"We reconstructed the dynamic landscape of the plain where the Indus civilization developed 5200 years ago, built its cities, and slowly disintegrated between 3900 and 3000 years ago," said Liviu Giosan, a geologist with Woods Hole Oceanographic Institution (WHOI) and lead author of the study published the week of May 28 in the Proceedings of the National Academy of Sciences. "Until now, speculations abounded about the links between this mysterious ancient culture and its life-giving mighty rivers."

Today, numerous remains of the Harappan settlements are located in a vast desert region far from any flowing river. In contrast to Egypt and Mesopotamia, which have long been part of the Western classical canon, this amazingly complex culture in South Asia with a population that at its peak may have reached 10 percent of the world's inhabitants, was completely forgotten until 1920's. Since then, a flurry of archaeological research in Pakistan and India has uncovered a sophisticated urban culture with myriad internal trade routes and well-established sea links with Mesopotamia, standards for building construction, sanitation systems, arts and crafts, and a yet-to-be deciphered writing system.

"We considered that it is high time for a team of interdisciplinary scientists to contribute to the debate about the enigmatic fate of these people," added Giosan.

The research was conducted between 2003 and 2008 in Pakistan, from the coast of the Arabian Sea into the fertile irrigated valleys of Punjab and the northern Thar Desert. The international team included scientists from the U.S., U.K., Pakistan, India, and Romania with specialties in geology, geomorphology, archaeology, and mathematics. By combining satellite photos and topographic data collected by the Shuttle Radar Topography Mission (SRTM), the researchers prepared and analyzed digital maps of landforms constructed by the Indus and neighboring rivers, which were then probed in the field by drilling, coring, and even manually-dug trenches. Collected samples were used to determine the sediments' origins, whether brought in and shaped by rivers or wind, and their age, in order to develop a chronology of landscape changes.

"Once we had this new information on the geological history, we could re-examine what we know about settlements, what crops people were planting and when, and how both agriculture and settlement patterns changed," said co-author Dorian Fuller, an archaeologist with University College London. "This brought new insights into the process of eastward population shift, the change towards many more small farming communities, and the decline of cities during late Harappan times."

The new study suggests that the decline in monsoon rains led to weakened river dynamics, and played a critical role both in the development and the collapse of the Harappan culture, which relied on river floods to fuel their agricultural surpluses.

From the new research, a compelling picture of 10,000 years of changing landscapes emerges. Before the plain was massively settled, the wild and forceful Indus and its tributaries flowing from the Himalaya cut valleys into their own deposits and left high "interfluvial" stretches of land between them. In the east, reliable monsoon rains sustained perennial rivers that crisscrossed the desert leaving behind their sedimentary deposits across a broad region.

Among the most striking features the researchers identified is a mounded plain, 10 to 20 meters high, over 100 kilometers wide, and running almost 1000 kilometers along the Indus, they call the "Indus mega-ridge," built by the river as it purged itself of sediment along its lower course.

"At this scale, nothing similar has ever been described in the geomorphological literature," said Giosan. "The mega-ridge is a surprising indicator of the stability of Indus plain landscape over the last four millennia. Remains of Harappan settlements still lie at the surface of the ridge, rather than being buried underground."

Mapped on top of the vast Indo-Gangetic Plain, the archaeological and geological data shows instead that settlements bloomed along the Indus from the coast to the hills fronting the Himalayas, as weakened monsoons and reduced run-off from the mountains tamed the wild Indus and its Himalayan tributaries enough to enable agriculture along their banks.

"The Harappans were an enterprising people taking advantage of a window of opportunity -- a kind of "Goldilocks civilization," said Giosan. "As monsoon drying subdued devastating floods, the land nearby the rivers -- still fed with water and rich silt -- was just right for agriculture. This lasted for almost 2,000 years, but continued aridification closed this favorable window in the end."

In another major finding, the researchers believe they have settled a long controversy about the fate of a mythical river, the Sarasvati. The Vedas, ancient Indian scriptures composed in Sanskrit over 3000 years ago, describe the region west of the Ganges as "the land of seven rivers." Easily recognizable are the Indus and its current tributaries, but the Sarasvati, portrayed as "surpassing in majesty and might all other waters" and "pure in her course from mountains to the ocean," was lost. Based on scriptural descriptions, it was believed that the Sarasvati was fed by perennial glaciers in the Himalayas. Today, the Ghaggar, an intermittent river that flows only during strong monsoons and dissipates into the desert along the dried course of Hakra valley, is thought to best approximate the location of the mythic Sarasvati, but its Himalayan origin and whether it was active during Vedic times remain controversial.

Archaeological evidence supports the Ghaggar-Hakra as the location of intensive settlement during Harappan times. The geological evidence -- sediments, topography -- shows that rivers were indeed sizable and highly active in this region, but most likely due to strong monsoons. There is no evidence of wide incised valleys like along the Indus and its tributaries and there is no cut-through, incised connections to either of the two nearby Himalayan-fed rivers of Sutlej and Yamuna. The new research argues that these crucial differences prove that the Sarasvati (Ghaggar-Hakra) was not Himalayan-fed, but a perennial monsoon-supported watercourse, and that aridification reduced it to short seasonal flows.

By 3900 years ago, their rivers drying, the Harappans had an escape route to the east toward the Ganges basin, where monsoon rains remained reliable.

"We can envision that this eastern shift involved a change to more localized forms of economy: smaller communities supported by local rain-fed farming and dwindling streams," said Fuller. "This may have produced smaller surpluses, and would not have supported large cities, but would have been reliable."

Such a system was not favorable for the Indus civilization, which had been built on bumper crop surpluses along the Indus and the Ghaggar-Hakra rivers in the earlier wetter era. This dispersal of population meant that there was no longer a concentration of workforce to support urbanism. "Thus cities collapsed, but smaller agricultural communities were sustainable and flourished. Many of the urban arts, such as writing, faded away, but agriculture continued and actually diversified," said Fuller.

"An amazing amount of archaeological work has been accumulating over the last decades, but it's never been linked properly to the evolution of the fluvial landscape. We now see landscape dynamics as the crucial link between climate change and people," said Giosan. "Today the Indus system feeds the largest irrigation scheme in the world, immobilizing the river in channels and behind dams. If the monsoon were to increase in a warming world, as some predict, catastrophic floods such as the humanitarian disaster of 2010, would turn the current irrigation system, designed for a tamer river, obsolete."

Once extending more than 1 million square kilometers across the plains of the Indus River from the Arabian Sea to the Himalayas and the Ganges, over what is now Pakistan, northwest India and eastern Afghanistan, the Indus civilization was the largest—but least known—of the first great urban cultures that also included Egypt and Mesopotamia. Named for one of their largest cities, the Harappans relied on river floods to fuel their agricultural surpluses. Today, numerous remains of the Harappan settlements are located in a vast desert region far from any flowing river. (Credit: Liviu Giosan, Woods Hole Oceanographic Institution; Stefan Constantinescu, University of Bucharest; James P.M. Syvitski, University of Colorado.)

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Milky Way will be hit head-onAndromeda galaxy will smash directly into ours

By Alexandra WitzeWeb edition : 4:26 pm

The monstrous Andromeda galaxy and the Milky Way are destined to hit head-on, not in a glancing blow, new observations from the Hubble Space Telescope show.

By precisely locating the same stars in Andromeda in 2002 and then again in 2010, astronomers at the Space Telescope Science Institute in Baltimore have calculated how the galaxy has moved against the background of deep space — confirming that the galaxy’s sideways motion is but a fraction of the speed at which it’s hurtling toward the Milky Way.

Andromeda is 2.5 million light-years away and closing in on the Milky Way at 250,000 miles per hour. The cosmic collision will transform the heavens into a hallucinogenic swirl 4 billion years from now. Calculations suggest that the sun will be tossed out during this galactic mash-up, to drift erratically in the eventual single, large galaxy that will coalesce from the two.

The work will appear in an upcoming Astrophysical Journal.

Four billion years from now, a collision between the Milky Way (left) and Andromeda (right) galaxies will have ripped out streams of stars, warped the galactic shapes and turned Earth’s night sky into a dramatic swirl of starlight.Credit: NASA, ESA, Z. Levay and R. van der Marel/STScI, A. Mellinger

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Quantum information has leapt through the air about 100 kilometers or more in two new experiments, farther and with greater fidelity than ever before. The research brings truly long-distance quantum communication networks, in which satellites could beam encrypted information around the globe, closer to reality.

Both studies involve quantum teleportation, which transports the quantum state of one particle onto another. This Star Trek–like feat is possible because of a phenomenon called entanglement, in which pairs of particles become linked in such a way that measuring a certain property of one instantly determines the same property for the other, even if separated by large distances.

In teleportation, two people — physicists call them Alice and Bob — share one each of a pair of entangled particles. Alice measures a property on her particle and sends Bob a note, through regular channels, about what she did. Bob then knows how to alter his own particle to match Alice’s. Bob’s particle then possesses the information that had been contained in Alice’s, which was obliterated by her measurement. Thus the information has been “teleported” from Alice’s lab to Bob’s.

Physicists first teleported quantum information in 1997 using a single pair of entangled photons, or particles of light. Since then researchers have slowly upped the ante, teleporting with larger groups of photons, over longer distances and sometimes using atoms as the entangled particles.

In 2007 Anton Zeilinger of the University of Vienna and his colleagues set a distance record by using a pair of entangled photons to transmit a piece of quantum information over 143 kilometers, between two of the Canary Islands. In new work, posted online May 17 at arXiv.org, the team reports a cleaner and more robust version of the same experiment using multiple entangled photons.

This time around, the scientists added a phase shift into the laser beams that made the final measurement cleaner and easier to pick out from background signals. The technique, called “active feed-forward,” is “an essential ingredient in future applications such as communication between quantum computers,” Zeilinger and his colleagues wrote. Team members declined interviews because the paper is not yet published.

“Our experiment confirms the maturity and applicability of the involved technologies in real-world scenarios, and is a milestone towards future satellite-based quantum teleportation,” they wrote.

In the second experiment, Chinese researchers entangled many photons together and teleported information 97 kilometers across a lake in China. That’s two orders of magnitude farther than any other multiphoton teleportation experiment, say Jian-Wei Pan of the University of Science and Technology of China in Shanghai and his colleagues. The work appeared online May 9 on arXiv.org.

Pan’s team also developed a way to track moving teleportation signals more accurately, which again could help make the final result more robust. “Our results show that even with high-loss ground to satellite uplink channels, quantum teleportation can be realized,” the scientists wrote.

Both Zeilinger and Pan next want to teleport information to a satellite in low-earth orbit. That distance is about three times that already accomplished in the Canary Islands, but because there are fewer air molecules to interfere with the signals at higher altitudes it may be easier to do.

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Plate Tectonics Cannot Explain Dynamics of Earth and Crust Formation More Than Three Billion Years Ago

ScienceDaily (June 1, 2012) — The current theory of continental drift provides a good model for understanding terrestrial processes through history. However, while plate tectonics is able to successfully shed light on processes up to 3 billion years ago, the theory isn't sufficient in explaining the dynamics of Earth and crust formation before that point and through to the earliest formation of planet, some 4.6 billion years ago. This is the conclusion of Tomas Naæraa of the Nordic Center for Earth Evolution at the Natural History Museum of Denmark, a part of the University of Copenhagen. His new doctoral dissertation has just been published by the journal Nature.

"Using radiometric dating, one can observe that Earth's oldest continents were created in geodynamic environments which were markedly different than current environments characterised by plate tectonics. Therefore, plate tectonics as we know it today is not a good model for understanding the processes at play during the earliest episodes of Earths's history, those beyond 3 billion years ago. There was another crust dynamic and crust formation that occurred under other processes," explains Tomas Næraa, who has been a PhD student at the Natural History Museum of Denmark and the Geological Survey of Denmark and Greenland -- GEUS.

Plate tectonics is a theory of continental drift and sea floor spreading. A wide range of phenomena from volcanism, earthquakes and undersea earthquakes (and pursuant tsunamis) to variations in climate and species development on Earth can be explained by the plate tectonics model, globally recognized during the 1960's. Tomas Næraa can now demonstrate that the half-century old model no longer suffices.

"Plate tectonics theory can be applied to about 3 billion years of the Earth's history. However, the Earth is older, up to 4.567 billion years old. We can now demonstrate that there has been a significant shift in the Earth's dynamics. Thus, the Earth, under the first third of its history, developed under conditions other than what can be explained using the plate tectonics model," explains Tomas Næraa. Tomas is currently employed as a project researcher at GEUS.

Central research topic for 30 years

Since 2006, the 40-year-old Tomas Næraa has conducted studies of rocks sourced in the 3.85 billion year-old bedrock of the Nuuk region in West Greenland. Using isotopes of the element hafnium (Hf), he has managed to shed light upon a research topic that has puzzled geologists around the world for 30 years. Næraa's instructor, Professor Minik Rosing of the Natural History Museum of Denmark considers Næraa's dissertation a seminal work:

"We have come to understand the context of the Earth's and continent's origins in an entirely new way. Climate and nutrient cycles which nourish all terrestrial organisms are driven by plate tectonics. So, if the Earth's crust formation was controlled and initiated by other factors, we need to find out what controlled climate and the environments in which life began and evolved 4 billion years ago. This fundamental understanding can be of great significance for the understanding of future climate change," says Minik Rosing, who adds that: "An enormous job waits ahead, and Næraas' dissertation is an epochal step."

“Plate tectonics theory can be applied to about 3 billion years of the Earth’s history. However, the Earth is older, up to 4.567 billion years old. We can now demonstrate that there has been a significant shift in the Earth’s dynamics. Thus, the Earth, under the first third of its history, developed under conditions other than what can be explained using the plate tectonics model,” explains Tomas Næraa. (Credit: Image courtesy of University of Copenhagen)

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Welcome to Animation Domination, Stone Age style. By about 30,000 years ago, Europeans were using cartoon-like techniques to give observers the impression that lions and other wild beasts were charging across cave walls, two French investigators find.

Ancient artists created graphic stories in caves and illusions of moving animals on rotating bone disks, say archaeologist Marc Azéma of the University of Toulouse–Le Mirail in France and Florent Rivère, an independent artist based in Foix, France.

“Stone Age artists intended to give life to their images,” Azéma says. “The majority of cave drawings show animals in action.”

Flickering torches passed over painted scenes would have heightened onlookers’ sense of seeing live-action stories, the researchers suggest in the June Antiquity.

Azéma and Rivère summarize their 20 years of research on Stone Age animation techniques, much of it previously published in French, in the new paper. They also describe for the first time examples of animation at two French caves, Chauvet and La Baume Latrone.

“Movement and action are indeed represented in cave art in different manners,” remarks archaeologist Jean Clottes, a rock-art specialist who now serves as honorary conservator general of heritage for the French Ministry of Culture. Clottes led a 1998 investigation of Chauvet’s 30,000-year-old cave paintings.

A 10-meter-long Chauvet painting represents a hunting story, Azéma proposes. The story begins by showing several lions, ears back and heads lowered, stalking prey. Mammoths and other animals appear nearby. In a second section of the painting, a pride of 16 lions, some drawn smaller than the rest to appear farther away, lunge toward fleeing bison.

Stone Age artists meant to depict animal movement in such scenes, Azéma says. An eight-legged bison at Chauvet, for example, resulted from superimposing two images of the creature in different stances to create the appearance of running.

In France, 53 figures in 12 caves superimpose two or more images to represent running, head tossing and tail shaking. At the famous Lascaux Cave, 20 painted animals display multiple heads, legs or tails.

A carving on an animal bone from another Stone Age cave in France depicts three freeze-frame images of a running lion, another way to represent motion.

Ancient Europeans also invented a kind of animation toy, the researchers suggest. Sites in France and Spain have yielded stone and bone disks, typically with center holes, showing opposing images of sitting and standing animals.

In experiments conducted since 2007, Rivère has reproduced these engraved disks and looped strands of animal tendon through the center holes. By twisting these strands, the disks rotate back and forth rapidly enough to make animals appear to be sitting down and standing up.

That’s the principle behind the thaumatrope, a device invented (or perhaps reinvented) in 1825. Two strings attached to the ends of a disk or card with an image on each side — say, a vase opposite a bouquet of flowers — were twirled between the fingers, so that the rotating pictures appeared to combine into a single image, such as flowers in a vase.

Thaumatropes are considered precursors of movie cameras and animation.

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How a mosquito survives a raindrop hitLightweight insects can ride water droplets, as long as they separate in time

By Susan MiliusWeb edition : Monday, June 4th, 2012

A raindrop hitting a mosquito in flight is like a midair collision between a human and a bus. Except that the mosquito survives.

New experiments show how the insect’s light weight works in its favor, says engineer David Hu of the Georgia Institute of Technology in Atlanta. In essence, the (relatively) huge, fast drop doesn’t transfer much of its momentum to a little wisp of an insect. Instead the falling droplet sweeps the insect along on the downward plunge. As Hu puts it, the mosquito “just rides the drop.”

The trick is breaking away from that drop before it and the insect splash into the ground. Mosquitoes that separate themselves in time easily survive a raindrop strike, Hu and his colleagues report online June 4 in the Proceedings of the National Academy of Sciences.

Such studies help reveal how animals evolved to take advantage of flight, says biologist Tyson Hedrick of the University of North Carolina at Chapel Hill. Mosquito tricks may also inspire engineers designing swarms of tiny flying robots, or interest physicists and mathematicians studying complex fluid dynamics at this scale.

Plenty of lab work has investigated how flying animals recover from disturbances, but there’s little work on raindrops because those collisions are very hard to study, Hu says. To mimic raindrop speed of about 9 meters per second, he and his colleagues tried dripping water off the third floor of a building toward ground-level mosquitoes. “It’s the worst game of darts you can imagine,” he says. “You have no hope of hitting them.”

Finally, Hu sprayed streams of water from a pump at caged lab mosquitoes and then refined the process by spraying mosquito-sized beads. His team found that mosquitoes hit with water survived using an insect version of tai chi: Move with the blow instead of resisting it. A raindrop can reach 50 times the mass of a mosquito, and after colliding, “the mosquito becomes a stowaway,” Hu says.

The wild ride comes with danger. Mosquitoes hitchhiking on water experience acceleration 100 to 300 times the force of Earth’s gravity, the researchers found. The previous champs for surviving acceleration had been jumping fleas, at a mere 130 times Earth’s gravity.

Such studies suggest insects are making tradeoffs, Hedrick says. Mosquitoes’ small mass might allow them fly through raindrops but leave them more vulnerable to other menaces, such as wind. Larger and heavier horseflies “should have no problem with wind but might be more disturbed by raindrop impacts,” he says.

Scientists who work in the field know how readily mosquitoes can survive wet weather. “I’ve worked in the field many rainy nights,” says entomologist Nathan Burkett-Cadena of the University of South Florida in Tampa, “and received zero respite from mosquitoes during even heavy rains.”

A mosquito survives being walloped by a raindrop by riding along on its descent to the ground, scientists have found. Credit: Courtesy Tim Nowack, Andrew Dickerson and David Hu/Georgia Tech

Water drops slamming into insects can knock them partly or completely off course, this laboratory video shows.

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When the Kepler spacecraft finds a giant planet closely orbiting a star, there’s a one in three chance that it’s not really a planet at all.

At least, that’s the case according to a new study that put some of Kepler’s thousands of candidate planets to the test using a complementary method for discovering celestial objects in stellar orbits. The results, posted June 5 on arXiv.org, suggest that 35 percent of candidate giants snuggled close to bright stars are impostors, known in the planet-hunting business as false-positives.

“Estimating the Kepler false-positive rate is one of the most burning questions in this field,” says astronomer Jean-Michel Désert of the Harvard-Smithsonian Center for Astrophysics, who has performed similar calculations for smaller planets.

Estimates by Désert and others place the false-positive rate at less than 10 percent, which isn’t necessarily contradictory given the different target populations of various research efforts.

“We cannot say anything about smaller planets,” says Alexandre Santerne, a graduate student at the University of Aix-Marseille in France and coauthor of the arXiv.org paper. “It’s just for giant planets close-in.”

Kepler looks for the periodic dimming of starlight produced by planets passing between Earth and their home stars near the constellation Cygnus. But not everything that darkens a star is a planet; smaller stars, for example, might masquerade as a planet. Instead of detecting periodic twinkles, Santerne and his colleagues looked for gyrations in host stars, the wiggles produced by orbiting planets’ gravitational tugs. Since heavy, nearby planets yank more noticeably on their stars, the team focused on giant candidates with orbits of 25 days or less.

Out of more than 2,300 possible planets, only 46 fell into that category. Eleven of these were already known planets. Santerne’s team confirmed nine more.

The remaining 26 candidates included 13 unknowns, two failed brown dwarf stars, and 11 members of binary star systems. “These can mimic clearly a planetary transit event,” says Santerne. “That’s why it’s so important to distinguish these things when you want to study planets and transits from the Kepler mission.”

After distributing the unknowns according to the observed ratios of objects, the team arrived at the 35 percent false-positive rate.

That number might seem high when compared with previous estimates, but scientists don’t consider it a serious flaw for Kepler. “This false-positive percentage is very low compared to all other transit programs,” says study coauthor and astronomer Claire Moutou, also at the University of Aix-Marseille.

The authors point to a discrepancy between their result and a 2011 study done by Timothy Morton and John Johnson at Caltech, who found a false positive rate closer to 5 percent. But comparisons between the two studies might not be so simple, Morton says, noting that the two groups calculated different things. Instead of looking at impostor rates in a specific population of planets, Morton determined the probability that any candidate — plucked from the sea of twinkling candidates — was real. He also excluded data from obvious impostors.

“Everything here is sort of a game of probabilities,” Morton says, pointing to the abundance of candidates. “It will be impossible to confirm them all with observations.”

As for current estimates of billions and billions of planets in the Milky Way, Moutou says those numbers are still valid. “Short period transiting planets are exotic objects, we don’t expect them to be everywhere,” she says. “The potential billion planets are more expected to be small, long-period planets. We didn’t kill those ones, fortunately.”